Wireless access links such as those provided by 3G and 4G networks are shared, limited resources. As such, they may become scarce as demand outstrips supply. As a consequence, contention will arise when too many users attempt to transmit data from their mobile devices within the same sector. Until recently, users predominantly uploaded considerably less data than they would download. However, the recent introduction of video-enabled mobile devices is likely to stimulate rapidly growing demand for uplink bandwidth.
For this and other reasons, there is a growing need for flexible methods of video transmission that can provide enough quality to satisfy user needs while consuming relatively little bandwidth during times when resources are scarce, and that can provide higher quality when resources are more plentiful.